The present invention refers, in a first aspect, to a surface layer adapted to form a cylinder barrel surface of a combustion engine cylinder block, the surface layer comprising separate phases of components that are separated from the phase and phases, respectively, of the remaining surface materials. In a second respect, the invention refers to a spraying powder suitable for producing such a surface layer, and in a third aspect, the invention also refers to a method of producing a surface layer adapted to form a cylinder barrel surface.
A thermal coating of cylinder barrel surfaces by means of plasma spraying is known in the prior art, e.g. from the document EP-B1-0,716,156 entitled xe2x80x9cCombustion Engine Block with Coated Cylinder Sleevesxe2x80x9d.
The machinability of such layers produced by plasma spraying by honing, lapping or grinding was limited up to now, with the result that the machining costs were relatively high, particularly as far as the machining time and the life span of the tools are concerned.
The machinability of such plasma spraying layers can be considerably improved by the addition of solid lubricating particles, for example by the addition of hexagonal boron nitride (BN), of MoS2 or WS2. Boron nitride or the mentioned sulfides, however, can be added to the layer only to a limited degree because the react with the oxygen of the ambient air or are corroded by the high temperature of the plasma. Thus, they have to be protected by costly envelopes.
Further, the document EP 99 81 1122.3 discloses a method of so-called xe2x80x9creactive sprayingxe2x80x9d in which, by means of controlled addition of oxygen during the plasma spraying process, FeO-(wustites) and Fe3O4-crystals (magnetite) are formed in the plasma spraying layer. Thereby, the coefficient of friction and the machinability are improved.
Finally, the document GB-A-2,297,053 discloses an insertable sleeve member for cylinder barrels that consist of a supereutectic aluminum/silicon-alloy. The sleeve member undergoes, after having been inserted into an engine block, a mechanical machining insofar as its surface is first coarsely and then finely machined. In a last phase of machining, the surface is honed. After the honing operation, those particles that are harder than the micro structure of the base alloy, particularly silicon crystals and intermetallic phases, slightly tower above the real surface of the sleeve member. By means of those exposed particles, the resistance to wear is said to be improved.
Based on that prior art, it is an object of the present invention to provide a surface layer forming a cylinder barrel surface that can be easily applied to the cylinder surface and that is considerably easier to machine, without negatively influencing other important characteristics of the layer material. In particular, the resistance to wear and the low coefficient of friction vis-à-vis the material of the piston rings cooperating with the surface layer shall be maintained or even improved.
It is a further object of the present invention to provide a spraying powder for producing surface layers having the above characteristics, and, finally, it is a still further object of the invention to provide a method of applying a surface layer having the above characteristics.
To meet these and other objects, the invention provides a surface layer adapted to form a cylinder barrel surface of a combustion engine cylinder block. The surface layer comprises separate phases of components that are separated from the phase and phases, respectively, of the remaining surface materials. The surface layer is formed by plasma spraying an iron containing spraying powder containing all components of the surface layer to be formed.
The surface layer can be applied either directly to a cylinder wall of an engine block, or to the wall of a cylinder sleeve member to be inserted in to the engine block.
Besides a predominant portion of iron, preferred further components of the coating powder are chrome, manganese, sulfur and carbon. Also suitable are bismuth, lead, tellurium and selenium. The afore mentioned materials can be added in their elementary form or in the form of compositions.
The above mentioned additions form the separate phases upon cooling of the surface layer applied by plasma spraying. Thereby, it is understood that the sprayed-on surface layer has the same composition as the spraying powder.
The spraying powder for producing a surface layer adapted to form a cylinder barrel surface of a combustion engine cylinder block comprises separate phases of components that are separated from the phase and phases, respectively, of the remaining surface materials. The surface layer is formed by plasma spraying the spraying powder, using a rotating plasmatron, whereby the spraying powder contains all components of the surface layer to be formed.